The deep oxidation of CH.sub.4 and other organics to CO.sub.2 was studied widely in the 1960s and 1970s when it was hoped that a cheaper alternative to Pt/Al.sub.2 O.sub.3 could be found as a catalyst for the total combustion of hydrocarbons and CO in automobile exhausts. However, base transition metal oxides were found to be less active and less robust than Pt/Al.sub.2 O.sub.3. Catalysts for the Control of Automotive Pollutants (Advances in Chemistry Series 143); McEvoy, J.D., Ed.; American Chemical Society: Washington, D.C., 1974. .beta."-alumina which was not ion exchanged has been proposed for use in hydrogen based fuel cells "Fuel Cell Handbook", Van Nostrand and Reinholt, (1989), pp 308-10. The anodic oxidation of CH.sub.4 in CH.sub.4 -air fuel cells have not been commercially practical because suitable electrocatalysts are unavailable. Most fuel cells utilizing CH.sub.4 use the steam reforming reaction (1) to pre-form more EQU CH.sub.4 +H.sub.2 O.fwdarw.CO+3 H.sub.2
easily oxidizable CO and H.sub.2. Appleby, A. J.; Foulkes, F. R. Fuel Cell Handbook; Van Nostrand Reinholt: New York, 1989. Recently, Steele and co-workers used an undisclosed electronically conducting metal oxide (Pt was found to be a poor catalyst) for the anodic oxidation of CH.sub.4 in a CH.sub.4 /He - air cell with a Y.sub.2 O.sub.3 stabilized ZrO.sub.2 electrolyte at 800 C. Steele, B. C. H.; Kelly, I.: Middleton, H.; Rudkin, R. Solid State Ionics 1988, 28-30, 1547. The steam reforming reaction greatly decreases the efficiency and increases the complexity of the cell. Of course, for use in a fuel cell the catalyst must efficiently oxidize methane in the absence of gas-phase oxygen. Other fuel cells operating on hydrogen employ phosphoric acid, molten carbonates or alkaline electrolytes which are liquids. In general, prior art fuel cells based on methane and other organics involve high operating temperatures and/or the use of hydrogen which presents problems of safety and containment.
A class of metal oxides which we have found to be of significant benefit in the direct deep oxidation of methane and other organic in fuel cells are the transition metal exchanged .beta."-aluminas. These metal oxide compositions are discussed in Barrie, J. D.; Dunn, B.; Stafsudd, O. M.; Farrington, G. C. Solid State Ionics 1986, 18-19, 677. These materials are unique in being the only oxides that are fast conductors of transition metal ions. The high mobility of these ions is believed to be due to the unusual structure of .beta."-alumina. It consists of layers of close-packed Al and O ions, called "spinel blocks", which are bridged by "columnar oxygens". The .beta."-alumina phase is generally stabilized by substituting a few % of the Al cations by Mg or Li. We have discovered that the ionic conductivity of such a catalyst appears to be useful in a fuel cell based on methane and other organics. While not bound by any theory, this may be due to the oxo-transition metal which can effectively "drag" O.sup.2 - through the conduction channels. No reports of catalytic studies on any such materials have appeared. The present invention pertains to findings applicable to the reactivity of transition metal exchanged .beta."-aluminas toward methane and other organics. The fuel cells of the present invention do not rely upon the presence of hydrogen, operate at relatively low temperatures, and are all solid. Hence, they are particularly adapted to be portable and are not prone to contamination.